Impaired mobility in Parkinson's disease (PD) is associated with decreased independence, reduced quality of life, and increased risk for falls, leading people with PD to identify mobility limitations as one of the worst aspects of the disease. There is incomplete understanding of the factors that contribute to walking limitations in PD, which hampers the development of effective rehabilitation strategies in this population. Walking abnormalities in PD are traditionally considered a motor impairment;however, motor deficits are only one of many factors contributing to limited mobility. Research using dual task paradigms has demonstrated that the control of walking is not completely automatic, but requires some degree of attention. Walking is disrupted by the performance of concurrent cognitive or motor tasks in many populations, including PD, suggesting that attentional processes and related aspects of cognition are critical to safe and independent mobility. The effects of PD on the neural mechanisms involved in the allocation of attention and the automatic control of walking are not well understood. Therefore, the long term goals of this research are (1) to develop a better understanding of the effects of PD on attention allocation and task prioritization when walking and performing a concurrent cognitive task and (2) to translate this knowledge into improved therapeutic interventions for walking limitations in this population. The proposed experiments examine the effects of PD on attention allocation and the automatic control of walking under dual task conditions (Specific Aim 1), the effect of anti-Parkinson medications (Specific Aim 2) and disease progression (Specific Aim 3) on the interaction of attention and walking, and the ability of people with PD to modify attention allocation based on changing environmental demands or explicit instructions (Specific Aim 4). For all Aims, changes in cognitive task speed and accuracy and walking speed and stability will be used to assess dual task interference in people with PD compared to age- and gender-matched controls. The goal of this Mentored Research Scientist Career Development Award is to provide the candidate with comprehensive training in the field of rehabilitation research through a combination of didactic work, intensive mentorship, and focused research experience. This award will provide the candidate with unique knowledge and skills that will promote an independent research career in both mechanistic research related to movement dysfunction in PD and translational research aimed at improved rehabilitation strategies for functional mobility. Public Health Relevance: For people with PD, walking impairments can lead to reduced mobility and independence, poor quality of life, and increased risk of falling. A better understanding of the effects of PD on attention allocation and the automatic control of walking is critical to the development of improved rehabilitation for walking and functional mobility in this population.